We are examining theoretical aspects of the structure, function, and evolution of proteins, with emphasis upon those areas where a high- speed digital computer is useful. We maintain a handbook of all protein sequences so far published, the Atlas of Protein Sequence and Structure. We are developing methods for the retrieval of various kinds of information from this collection. Automated methods are being developed and applied for the construction of evolutionary trees from homologous protein sequences. A phylogenetic tree derived from the data in many families of sequences is also being constructed. Quantitative measures of the degree of relatedness of proteins are being investigated and applied to the data. We are collecting data on the occurrence of the various kinds of mutations and developing an improved model of the point mutation and chromosomal aberration processes.